The present invention relates to an oil pump which supplies lubricating oil to each part of sliding portions in a piston, a valve system, or the like for an internal combustion engine etc., and more specially, to an oil pump which is capable of improving lubricity.
In recent years, there have been proposed and developed various oil pumps, such as a trochoid pump generally known and used, for lubrication of engine. One such oil pump for lubrication of engine has been disclosed in Japanese Patent Provisional Publication No. 2003-239869 (hereinafter is referred to as “JP2003-239869”).
The oil pump disclosed in JP2003-239869 comprises a pump housing, an working chamber formed in the pump housing, an outer rotor with a plurality of internal teeth integrally formed with the inner circumference thereof, which is rotatably housed in the working chamber, an inner rotor with a plurality of external teeth integrally formed with the outer circumference thereof and meshing with the internal teeth of the outer rotor, which is rotatably housed in the working chamber, and a drive shaft rotating and driving the inner rotor, which is rotatably housed in the pump housing.
As the inner rotor turns via the drive shaft, the outer rotor also turns in response. And then, the volume of a pumping chamber formed by the mesh of the internal and external teeth varies, it forces oil to flow from a suction port into the pumping chamber, and to flow toward a discharge port. Thus, this oil pump works as a pump supplying lubricating oil to each part of sliding portions in an internal combustion engine.
The drive shaft is rotatably supported on an inner peripheral surface of a journal formed in the pump housing. Between the drive shaft and the journal, a first groove and a second groove are provided. The first groove has its one end communicating with the discharge port and the other end reaching the halfway of the journal. The second groove has its one end communicating with the outside of the pump housing and the other end finished in the halfway of the journal.
These first and second grooves are arranged so that both of the grooves are spaced apart from each other, and a part of each the groove is overlapped to each other in the groove extending direction.
Accordingly, when the engine starts, air which has accumulated in the discharge port is discharged rapidly. Additionally, during operation of lubricating, oil having flowed out or spilled out from the discharge port flows into the first groove, and further flows into the second groove from the first groove through a sliding clearance space between an outer peripheral surface of the drive shaft and the inner peripheral surface of the journal. Simultaneously, the sliding clearance space between the outer peripheral surface of the drive shaft and the inner peripheral surface of the journal is lubricated by way of the above oil flow.